Here is the 2010 Flying Cloud manual according to the Airstream site:
https://www.airstream.com/wp-content...gcloud2010.pdf
And here is the 2011 manual:
https://www.airstream.com/wp-content...gcloud2011.pdf
. . . which does list a 30' on p. I-1 [PDF p. 109/113]
On p. F-7 in the plumbing section it also lists a 30' for the pump location. [PDF p. 73/113]
My guess would be that your 2010 FC30 was manufactured at the end of the model year, and just did not get labeled exactly right, nor have the proper manual. A careful examination of VIN's would probably be further evidence IMO.
Does the second manual linked above seem right for your floor plan?
Good luck!
Peter
PS -- This is probably not the only error or omission you will find [not] in the manual!